How to grade a star?

We have the habit of rating all restaurants with "Stars". Ever wondered how one rates a star?
The brightness of a star seems a likely choice for the rating.




In any star map the constellations are marked and the stars are generally denoted with Greek letters. It is based on the brightness of that star in that constellation. In any constellation, the brightest star is labelled alpha, the second bright star is named beta so on and so forth. Suppose the constellation has all the stars of equal brightness, like Ursa Major, then the naming begins from the head of the constellation.




This is with respect to constellations. But how is the brightness of any star measured?
Some questions that haunt me at this time:
Is the brightness of a star dependent on its temperature?
Would the distance of the star from the observing point determine its brightness?
Would the composition of the star contribute?
How exactly do we measure the brightness of a star?

Will be back soon :)